The present invention is directed to improvements in the current "backline" operations, wherein primary explosives, e.g. lead azide, lead styphnate and tetracene, are transferred from shipping containers, processed, i.e. filtered, washed and dried, and transferred to the bowls used in loading of detonators and similar devices.
The backline operations are essentially the same for all primary explosives and these procedures have changed only slightly since these explosives were first used in military items. The current process is relatively time-consuming, expensive, and because of the nature of the process is hazardous to personnel working on the backline.
At present, the backline operation is a batch process performed manually in a series of separated small buildings using laboratory sized equipment. Lead azide and lead styphanate are shipped in drums with up to 150 pounds of explosive contained in a large rubber (or plastic) bag packed in sawdust wet with a water-alcohol solution in an outer burlap bag. The large rubber (or plastic) bag contains from 2 to 14 bags of explosives (the number and weight of explosives in these inner bags depends on the vendor) commonly containing from 10 to 25 pounds of explosives.
Tetracene is shipped in a 30-gallon metal container with two 12.5-pound bags of tetracene inside one large bag. Packing material is the same as for lead azide and lead styphnate, sawdust, and a water-alcohol solution.
In present operations, the outer bag is opened, sawdust and water removed, the rubber (or plastic) bag opened, and an inner bag is transferred to a container containing enough liquid to cover the bag. When ready to process, the bag (kept wet with alcohol) is kneaded to break up lumps and the explosive is transferred from the bag. All packing material is returned to the shipping drum and a kill solution added. After an appropriate waiting period, the drum is moved to a disposal area and the contents discarded.
After removal from the bag, approximately 2 pounds of the explosive is transferred (in some cases directly from the bag) to a large Buchner filter, the water-alcohol removed and the resultant cake washed with ethanol to remove the water, taking care to ensure that the wash liquid goes through the explosive and that explosive is not allowed to dry out in the filter. The damp explosive is transferred to drying tubes after manually breaking up the filter cake.
After drying at 120.degree. F., the explosive is transferred to the screening building where it is remotely transferred to a conical cloth screen (jelly bag). Screening is accomplished by up and down movement of the conical cloth screen and the screened explosive goes into an approximately 2-pound container. The next operation in the case of lead azide to be used in detonators and similar items is rebowling in which 2 pounds of lead azide is transferred to the smaller cups used on the detonator loading line or machines. Lead azide is to be used in blends; lead styphnate and tetracene are not rebowled and stay in the 2-pound containers until weighed remotely.